Storage batteries which have been prevailingly used are, as well known, a nickel-cadmium storage battery and a lead storage battery. As the range of their use have been increasing in recent years, however, the development of storage batteries having lighter weight, higher capacitance and higher energy density has come to be desired eagerly.
Quite recently, a metal-hydrogen alkali storage battery wherein a hydrogen absorbing alloy is used as a negative electrode and nickel hydride as a positive electrode has come into the limelight.
While such a nickel-hydrogen alkali storage battery is charged with electricity, the hydrogen absorbing alloy electrode electrolyzes the water in an alkali electrolytic solution and absorbs the hydrogen gas produced by the electrolysis. During the discharge, on the other hand, the hydrogen absorbing alloy electrode releases the hydrogen gas and, at the same time, oxidizes the hydrogen gas to return it to the state of water.
When the storage battery is overcharged for the purpose of rapid charging, however, not only oxygen gas is generated from the positive electrode but also hydrogen gas is generated from the negative electrode, and thereby the internal pressure of the storage battery is increased.
This is being the case, it has been proposed to design the negative electrode so as to have a greater charging capacity than the positive electrode, thereby generating oxygen gas preferentially upon charging. Therein, the oxygen gas generated preferentially is made to react with the hydrogen gas produced on the negative electrode to be converted into water; as a result, a rise in the internal pressure of the storage battery can be controlled.
An increase in the charging capacity of the negative electrode, although it can inhibit the increase in an internal pressure of the battery upon overcharging, has a defect that it requires correlatively a decrease in the volume occupied by the positive electrode in the storage battery to result in the lowering of the battery capacity.
For the purpose of obviating such a defect, it has been proposed to coat the electrode surface with a fluorine-containing water repellent to form thereon a three-phase interface of gas, liquid and solid, thereby making an improvement in hydrogen absorbing properties of the electrode (Japanese Tokkai Hei 2-250260 and Japanese Tokkai Hei 2-291665). In coating such a water repellent on the negative electrode, a solvent-insoluble resin, such as a polytetrafluoroethylene resin or a tetrafluoroethylene-hexafluoroethylene copolymer resin, has been used in the form of dispersion, so that the foregoing measure has a drawback of requiring much time and labor for formation and drying of the coat of water repellent.